The objective of the present Phase 1 feasibility study is to develop a quantitative serum-based biomarker for detecting neuronal damage in mild traumatic brain injury (TBI). Postconcussion Syndrome (PCS) is believed to be the cause for much if not all of the disability suffered by mild TBI patients. Although PCS occurs in about 40% of mild TBI patients, radiologic techniques detect few of these patients. The purpose of the proposed studies is to develop a new serum biomarker of neuronal damage for identifying mild TBI patients who subsequently develop PCS. We have developed a sandwich ELISA that quantifies a neuronally localized protein, MAP-tau, that is proteolytically cleaved and released from damaged neurons after brain injury (C-tau). In preliminary studies we demonstrate that serum C-tau levels are significantly elevated in mild TBI patients. The proposed studies will determine if initial serum C-tau levels predict which mild TBI patients subsequently develop PCS. Our Specific Aims are: Specific Aim 1: Determine if initial C-tau levels are a reliable predictor of Postconcussion Syndrome in mild TBI patients (N=80). Initial serum C-tau levels (<12 hrs postinjury), head CT (<12 hrs postinjury) and clinical-laboratory data are collected from mild TBI patients (ICD-9 850-854; GCS>12). Diagnosis of PCS is made at 3-month follow-up. Patients will be dichotomized by presence or absence of PCS. The serum C-tau cut-off for predicting PCS will be determined by ROC analysis and the sensitivity, specificity and predictive value of initial C-tau levels for predicting PCS determined. Specific Aim 2: Determine if initial C-tau levels predict intracranial injury in mild TBI patients. Similar analysis of Specific Aim 1 patients but patients dichotomized by presence or absence of CT abnormality. Specific Aim 3: Determine if initial C-tau levels are a reliable predictor of Postconcussion Syndrome in mild TBI patients with no CT abnormality. Similar analysis as for Specific Aim 1 but restricted to patients with no CT abnormality which is projected to be about 85% to 90% of all patients (N = approximately 70).